Herpes simplex virus 1 (HSV-1) and HSV-2 establish latency in different neuronal subtypes (A5+ and KH10+) in murine trigeminal ganglia, results which correlate with restricted productive infection in these neurons in vitro. HSV-2 latency-associated transcript (LAT) contains a cis-acting regulatory element near the transcription start site that promotes productive infection in A5+ neurons and a second element in exon 1 that inhibits productive infection in KH10+ neurons. HSV-1 contains no such regulatory sequences, demonstrating different mechanisms for regulating productive HSV infection in neurons.

Purpose

How herpes simplex virus (HSV) is transported from the infected neuron cell body to the axon terminal is poorly understood. Several viral proteins are candidates for regulating the process, but the evidence is controversial. We compared the results of Us9 deletions in two HSV strains (F and NS) using a novel quantitative assay to test the hypothesis that the viral protein Us9 regulates the delivery of viral DNA to the distal axon of retinal ganglion cells in vivo. We also deleted a nine-amino acid motif in the Us9 protein of F strain (Us9-30) to define the role of this domain in DNA delivery.

Methods

The vitreous chambers of murine eyes were infected with equivalent amounts of F or NS strains of HSV. At 3, 4, or 5 days post infection (dpi), both optic tracts (OT) were dissected and viral genome was quantified by qPCR.

Results

At 3 dpi, the F strain Us9- and Us9-30 mutants delivered less than 10% and 1%, respectively, of the viral DNA delivered after infection with the Us9R (control) strain. By 4 and 5 dpi, delivery of viral DNA had only partially recovered. Deletion of Us9 in NS-infected mice has a less obvious effect on delivery of new viral DNA to the distal OT. By 3 dpi the NS Us9-strain delivered 22% of the DNA that was delivered by the NS wt, and by 4 and 5 dpi the amount of Us9-viral DNA was 96% and 81%, respectively.

Conclusions

A highly conserved acidic cluster within the Us9 protein plays a critical role for genome transport to the distal axon. The transport is less dependent on Us9 expression in the NS than in the F strain virus. This assay can be used to compare transport efficiency in other neurotropic viral strains.